Material for treating oil well drilling fluids



fltates MATERIAL FOR TREATING H. WELL DRILLING FLUIDS William G. Van Beckum, Longview, Wash., assignor to Weyerhaeuser Timber Company, Tacoma, Wash., a corporation of Washington No Drawing. Application June 21, 1952, Serial No. 294,912

3 Claims. (Cl. 252-85) Loss of the well drilling fluid to the formation is known to the trade as loss of circulation, and the use of fibrous or bulky materials to prevent loss of circulation in oil well drilling operations is well known to the art. Hay, straw, sawdust, chopped bagasse, flax fiber and like materials have long been used for this purpose. The mechanics of their use has been to mix the additives with the mud in the pit and gun the mixture to some semblance of uniform consistency. When the fortified mud reaches the place in the well where it is lost to the formation, the bulky or fibrous material mats, crowds and otherwise seals off the openings and arrests the flow of mud from the well.

Generally, the material is not added to the oil well drilling fluid until needed, at which time it is important that the material be capable of fast addition to and incorporation in the mud; that it be of such nature that it will not clog pumps or the drill bit, and that it be capable of use with any of the three fundamental types of drilling fluids, e. g., oil, oil emulsions, or water base muds.

It is well known to the art that substances which are effective circulation loss preventatives in some formations are not useful in others. The effectiveness of the product is related, at least partially, to the particle size of the additives and the size of the openings in the faulty formation. Applicant has conceived of a product having a broad particle size range consisting of feltable fibers to cover large openings in the formation with a felted mat having small or tortuous openings, and a non-fibrous or,

non-feltable material capable of plugging small openings in the formation itself or filling the interstices in'the fiber belt. This product is effective to seal a wider range of formation porosities than either constituent alone, and is more effective in closing off large openings than when either ingredient is used by itself. The product is especially useful as a fibrous-type circulation loss preventative which may be shipped in bales or bags at an economical density, and which is made easily and readily applicable to the mud by incorporating in the fiber a non-fibrous material to prevent felting of the fiber in the package. The product possesses the important attribute of cleanliness, it lacks any offensive odor, it is not sub? 'ject to bacterial decomposition, and is available in constant supply in quantities sufficient to supply large demands therefor. A preferred product is of such nature that it is subject to controlled manufacture and composition.

One of the components of the lost circulation preventative is a fibrous material. Practical types of fibrous materials are wood fiber, bagasse, cellophane strips, and flax fiber. The instant invention is described herein with reference to wood fiber, and reference is made to U. S.

atent ice Asplund Patents No. 2,008,092 and No. 2,145,851, relating to the manufacture of wood fiber. In the Asplund process, wood chips are introduced into an atmosphere of steam at high pressure, providing a temperature above 212 F., at which the lignin content of the particular wood is softened to permit ready defibration by mechanical means. The chips quickly soften and are fed directly to a rotary defibering disc mechanism housed in said environment which mechanically rubs the softened chips to ultimate fibers or a predominance of such fi bers. The resulting defibered wood is then discharged to the atmosphere. There is no intention to limit the invention, where the fibrous material is of wood, to the use of Asplund defibrator fiber, since mechanically produced fibers, such as McMillan fiber, are satisfactory for use in the manufacture of lost circulation preventatives.

Wood fibers may be treated with materials inert to the well drilling fluid as, for example, with asphalt to collect and hold the fines created by the grinding operations, with borax, or with caustic solutions preparatory to the removal of lignins, polysaccharides and other soluble organic substances.

A second component of the lost circulation preventative material is a non-fibrous or non-feltable material incorporated with the packaged fiber to facilitate rapid fluifing of the baled or bagged material at the time it is to be added to the well drilling fluid. It will be understood that the compressed material, to be added to the well drilling fluid, must be broken apart and substantially disintegrated in order to be readily and completely dispersed in the drilling fluid.

One purpose of the non-fibrous or non-feltable material is to prevent the fibrous material from felting so tightly upon dense packaging thereof as to be difiicult to break apart. Practical types of non-fibrous materials useful for this purpose are sawdust, seed hulls such as cottonseed hulls, nut shells such as peanut shells, flax shives, and the substantially non-feltable portions of the bark of trees and especially the cork and bast fiber fractions of the bark.

A second function of the non-fibrous material is to plug small openings in the formation through which the well hole is drilled, and to fill and seal the interstices in the fiber felt which forms over larger openings in the formation. The meritorious performance of the mixture for this purpose is due to the wide range of particle size andshape, regardless of the exact nature of the materials used. It is important, however, and believed critical to the successful performance of materials embodying the invention, that one of the components of the lost circulation preventative provide a fibrous felt in which to incorporate the non-fibrous material.

It is an object of the invention to provide a material having a wide range of particle size and shape for bridg ing or sealing cracks, crevices, fissures and other porous or faulty earth formations encountered by the drill in well drilling operations to form a barrier for preventing further loss of the well drilling fluid to'the formation.

It is a further object of the invention to provide a material for treating well drilling fluids comprising a mixture of a fibrous material capable of forming a felt over cracks, crevices, fissures and other porous or faulty formations through which the well is drilled, and a nonfibrous material for enhancing breaking and fluffing bales or other dense packages of the fibrous material at the time of treating the Well drilling fluid.

It is a further object of the invention to provide a material for treating well drilling fluids comprising a mixture of fibrous and non-fibrous materials derived from trees.

It is a further object of the invention to provide a material for treating well drilling fluids comprising a material capable of forming a felt over cracks, crevices, fissures and other porous or faulty formations encountered by the drill, and a material for plugging and sealing openings in the felt.

It is a further object of the invention to provide a material for treating Well drilling fluids comprising a mixture of feltable fibers and the non-feltable constituents of the bark of trees.

It is a further object of the invention to provide a material for treating well drilling fluids comprising a mixture of wood fiber and the cork component of the bark of trees.

It is a further object of the invention to provide a method of treating well drilling fluids to provide a barrier for plugging or sealing cracks, crevices, fissures and other porous or faulty formations encountered by the drill to prevent further loss of well drilling fluids.

Various other and ancillary objects and advantages of the invention will become apparent from the following description of an illustrative embodiment of the invention and explanation of the manner of its use.

Wood fibers such as those produced by the Asplund defibrator disclosed and described in U. S. Letters Patent No. 2,008,092 and No. 2,145,851 are ideally suited to be added to well drilling fluids for the purpose of forming a densely felted mat over cracks, crevices, fissures and other porous or faulty formations which are encountered by the drill in oil well drilling operations. These fibers are made from wood which is chipped and defibered and flutfed to assure proper bridging characteristics. When added to the well drilling fluid, the fibers form a fibrous mat over gravelly, fractured and fissured formations and quickly become imbedded with mud to speedily form a tough seal to stop the flow of well drilling fluids from the bore. The fibers readily mix with the mud and stay in suspension until deposited to stop the loss of drilling fluid. It is preferred that wood fibers be treated with asphalt to collect and hold dust created by the defibering process so that the viscosity of the fluid is not disturbed by the addition of dust with the fiber.

Notwithstanding these properties of wood fiber and the obvious advantages attending its use, acceptance by the trade has been limited because of the difliculty of breaking up packages of compressed fiber fast enough when a problem of lost circulation called for immediate action. When packaged at a density economical for shipping, the fibers were so felted together that addition to the mud was difficult and slow. Various attempts were made to improve handlcability, one of which was to limit the packaged fiber to -l2 pounds per cubic foot density. Merchandising in bags was proposed. Notwithstanding these provisions, the low density material still presented disadvantages with respect to handlcability, and similar trouble'was encountered in pouring from the bags at the well.

Applicant has discovered that physical incorporation of quantities of a non-fibrous or non-feltable material in intimate mixture with the fiber prevents felting of the fiber package and so enables it to be quickly broken up and 'thefibers flufied for addition to the well drilling fluid, and, at the same time, make the product more effective for preventing lost circulation of oil well drilling fluids by broadening the particle size range and providing a greater variation of particle shapes.

Examples of non-fibrous materials which may be added to fiber to prevent felting of the compressed product are sawdust, seed hulls such as cottonseed hulls, nut shells such as peanut shells, flax shives, and the substantially non-feltable components of the bark of trees and especially the cork and bast fiber components of the bark. A product constituting from about 43 to 3% non-fibrous material, and from about to if; fibrous material, by weight, is particularly useful as a product for insuring pourability of the packaged material. As a practical matter, however, the composition is limited only by the amount of non-feltable material needed to insure pourability of the material from the package. It will be appreciated that the density to which the package is compressed is the controlling factor which determines the proportions of non-feltable material to fiber. The proportions given hereinabove are for densities of from 10 pounds to about 30 pounds per cubic foot.

A product constituting approximately -70% cork and 30-40% bast fiber or sclerenchyma tissue is particularly useful, both to prevent felting together of the fibers when the product is baled or bagged, and as a material for filling the interstices of the mat or felt created by deposition of the fibers over gravelly, fractured or fissured formations in the well bore. The cork provides flake or plate-like particles of a size which are retained on 14 mesh and 28 mesh screens, and a more granulated product of plusmesh screen size. The fiber content of the bark is made up of elongated fibers having a diameter such as will enable them to pass through a 65 mesh screen, and having a length of, roughly, ten diameters. These fibers are relatively stiff and differ sulficiently from wood fibers in structure and performance to provide an almost wholly dissimilar material. These bark fibers form a mat over porous portions of the wall of the bore and so augment the sealing properties of the wood fibers. The cork, for example, being neither fibrous in structure nor capable of being felted under conditions attending baling or bagging of the fiber, prevents the fibers from felting together and obviates the expenditure of time and effort to break up the bales and fluff the fiber at the time of adding the material to the drilling fluid. On the other hand, the mixture of fibrous and non-fibrous materials herein described may be poured from the bag into the pit adjacent the well and quickly dispersed in the mud. Other advantages attending the use of this material are that it is substantially inert insofar as the well drilling fluid is concerned; the material is not subject to bacterial decomposition and will not rot, deteriorate or sour, either during storage or in the hole; the material does not rope, nor does it break down through circulation, and stays in suspension in the mud until the presence of a crack, crevice, fissure, or other porous formation in the wall of the hole causes the material to be deposited in place to perform its intended function.

A mixture of fiber and cork and/ or comminuted whole bark contains particles of various sizes and shapes which coact to seal a larger range of openings in the wall of the bore than does fiber alone. Fiber, as the name implies,

is relatively long compared to its thickness or diameter whereas the cork particles are somewhat flat and thin, with the larger sizes being more or less plate-like and the smaller sizes somewhat granular. Comminuted wholebark particles are of varying shapes and sizes. The bark particles serve as fillers for the interstices in the fiber mat and enable the mat to more effectively seal the wall of'the bore against the loss of circulation therefrom. A mixture of wood fiber, cork and comminuted whole bark provides a large range of particle sizes and a great diversity of particle shapes. Utility of such a product is judged by the character of the formation wherein loss of drilling fluid occurs. Cork is a satisfactory plugging material for a porous formation, whereas fiber is more effective for sealing cracks. For large fissures the combined material is better than either one alone, the fibers forming a felt over the fissure and the cork and other particles plugging interstices in the felt.

On the other hand, by reason of the fact that either cork or wood fiber is by itself a satisfactory material for treating well drilling fluids to stop the loss of the mud to formationsencountered by the drill, and that for specific types of formations one or the other of these products will function as well or better than a mixture of the two, the proportions of these materials in a loss of circulation preventative may be said'to be in the range of from zero to 100 parts non-fibrous material to 100 to zero parts fiber. In most instances, a mixture of the two materials is a superior bridging material and, in addition, possesses the advantage of being easily and time is consumed, either in breaking apart highlycom pressed bales or in empting tightly packed bags, particularly when time is at a premium. Tightly compressed fibers are not easily separated, and expensive and cumquickly added to the bersome machines are required to flufl the material. drilling fluid. I Table III shows the comparative resistance to compres- Other bark and wood products may be used to replace sion of lost circulation fibers, and is a determination of approximately half of the cork in the wood-fiber cork the looseness of the bales. The procedure was to commixture. These materials are Silvacon 412, a mixture of press the fibers to the same volume or density and to approximately 40% cork and 60% bast fiber from the 10 measure the force required- The greater the force. the bark of the Douglas fir; ground whole bark; and wood more tightly the material would be packed in a bag. Two sawdust. These materials differ sufficiently from wood p t i s f t sts w r run; n t a 30 pounds per fiber in their physical aspects to come within the descripcubic feet y, and the other to a 10 Pounds P cubie tion of nonfeltable materials in the loss of circulation foot Y- It Will be noted that When finely ground mixture. For test purposes, whole bark used to replace Whole bark is us d t rep ace 5 0f th rk content approximately half of the cork content of the wood-fiber O e bale, approximately the same degree of loosecork mixture was ground through a in h screen t proness is achieved as when cork alone is used as the nonduce coarse material. For other test purposes, whole fibl'eus albark was ground through a A; inch screen to produce fine material. The physical properties of the batches TABLE III of ground whole bark are compared with plus-65 mesh Comparative r sistance to compression of lost screen cork in the following table: circulation fibers TABLE I A aranc Physlcal properties of ground whole bark f gg ig g gfg gg lone lb./eu.ft. to 10 lb./cu. fifjf t Screen Analysis (lb) 1b./cu. (it) Coarse Fine Wood Fiber over 10,000 251 semi-tight. (allund Ground Cork 3o 40% Fiber, 00% Cork 4, 850 08 very loose. ole Whole 40% Wood Fiber, 60% Coarse 7, 900 89 semi-loose. Bark Bark Ground Whole Bark.

40% Wood Fiber, 60% Finely 8, 600 104 semi-tight.

Ground Whole Bark. Plus-28 mesh .percent 69 40 77 40% Wood Fiber, 30% Cork, 6, 800 62 loose. Plus-65 mesh do 25 47 22 30% Coarse Ground Whole Plus-100 mesh "do. 4 8. 5 1 Bark. Bulk density (1lb./cu.ft.) 9. 6 13.4 15.5 Wood Fiber, 30% Cork, 6, 800 68 Do.

glgkFinely Ground Whole Tests were made to determine the effectiveness of the ggi g ggi gg t g 2 l z ig g xg zfzgzfi From the data in Table III, it is apparent that wood with 15 gol iiids per b zirrel of tlie f ollowin lost circula- 40 fiber by far the most tightly packed mammal and tion materials. g that a mlxture of wood fiber and cork packs the least. All other values lie much closer to the wood fiber and- (1) Regular 13-1645 40% Wood fiber: 60% cork cork values than they do to the wood fiber values. The 40% Wood fiber, 30% coarse-ground WhOle bark, conclusion is made that substitution of cork by other 30% cork materials such as ground whole bark will tend to increase 40% Wood fiber, 30% fine-ground Whole bark, 30% the tightness of a bag, the increase being directly proporcork tional to the reduction in amount and lack of range of Table II indicates that the mixture of wood fiber, cork particle size and variability in shape of the material suband ground whole bark is an eflicient lost circulation mastituted. It is apparent, however, that ground whole bark terial. The data indicate that the particle size of the can be used to replace cork to the extent of of the additive has a profound influence on the extent of loss cork normally used in the wood-fiber cork mixture. For of circulation. It will be appreciated, however, that varyexample, a lost circulation material having the composiing conditions in formations encountered by the drill call tion of 65% cork and 35% fibrous material may be for materials having a wide range of particle sizes and modified to have a maximum of approximately 30% shapes, and that the following test data are not indicaground whole bark, 30% cork, and 40% wood fiber. tive of the optimum particle sizes for all types of forma- Having now described my invention and in what mantions. ner the same may be used, what I claim as new and de- TABLE H sire to proteict by; Letters Paterit is :11 dnll fl d 1. A pro not or treating oi we ing ui s com- Fluza' loss through Nevada N0. 100 sand bed at 100 p. s. l. prising a mixture of Wood fiber and the comminuted cork component of the bark of trees, said cork being of plus Control g z f gg fi: 23%: -mesh size, the product being capable 0t forming a None 40% fib 30%; Coarse ine barrier for preventing loss of well drilling filllCl to cracks, Cork 63 $1 3, crevices, fissures and the like encountered by the drill, Berk Berk 65 the product being compressed to a density of from 10 pounds to about 30 pounds per cubic foot, the cork com- 2 lg g1 g8 ponent being present in an amount sufiicient to substan- 186 71.5 as 31 tially reduce felting of the compressed fiber and to engg g 5 2g 5 hance the dispersion of the fiber in the mud. 215.5 90.5 70.2 44 7O 2. A product for treating oil well drilling fluids comprising a mixture of wood fiber and a non-fibrous, non- As has been stated, one of the functions of the nonfeltable constituent of the bark of trees, the product being fibrous or non-feltable content of the herein described macapable of forming a barrier for preventing loss of well terial is to insure a loosely packed, easy to handle pack drilling fluid to cracks, crevices, fissures and the like enage. Wood fiber alone is easily felted, and too much countered by the drill, the product being compressed to in an amount sufiicient to substantially reduce felting ofv the compressed fiber and to enhance the dispersion of the fiber in the mud.

3. A product to be added to oil well drilling fluids to form a barrier for preventing loss of well drilling fluid to cracks, crevices, fissures and the like, comprising a mixture of from 30-40% wood fiber and from 60-70% of the cork component of the bark of trees, said cork being of plus-65 mesh size, the product being compressed to a density of from 10 pounds to about 30 pounds per cubic foot, the cork component being present in amount sufiicient to prevent felting of the compressed fiber.

References Cited in the file of thispatent UNITED STATES PATENTS 2,064,936 McQuiston Dec. 22, 1936 2,119,829 Parsons June 7, 1938 2,214,366 Freeland et a1 Sept. 10, 1940 2,599,745 Campbell et a1. June 10, 1952 2,601,050 Nestle June 17, 1952 2,610,149 Van Dyke Sept. 9, 1952 

1. A PRODUCT FOR TREATING OIL WELL DRILLING FLUIDS COMPRISING A MIXTURE OF WOOD FIBER AND THE COMMINUTED CORK COMPONENT OF THE BARK OF TREES, SAID CORK BEING OF PLUS 65-MESH SIZE, THE PRODUCT BEING CAPABLE OF FORMING A BARRIER FOR PREVENTING LOSS OF WELL DRILLING FLUID TO CRACKS, CREVICES, FISSURES AND THE LIKE ENCOUNTERED BY THE DRILL, THE PRODUCT BEING COMPRESSED TO A DENSITY OF FROM 10 POUNDS TO ABOUT 30 POUNDS PER CUBIC FOOT, THE CORK COMPONENT BEING PRESENT IN AN AMOUNT SUFFICIENT TO SUBSTANTIALLY REDUCE FELTING OF THE COMPRESSED FIBER AND TO ENHANCE THE DISPERSION OF THE FIBER IN THE MUD. 